Epoxy resins and cements are used in a variety of oil field applications, which include primary cementing, casing repair, and water control. Epoxy materials may also be used for cementing wells which are employed to dispose of liquid wastes. An operation of this type is disclosed in U.S. Pat. No. 4,072,194. Epoxys may also be used in the leaching of minerals from subterranean formations to repair leakage through short-circuit passages formed between adjacent injection and production wells. Such a use is disclosed in U.S Pat. No. 4,438,976. Epoxy systems have high compressive strengths and excellent resistance to chemical and thermal degradation. Therefore, epoxys are well suited for the hostile conditions often encountered in subterranean formations.
In most applications, the epoxy formulations are based on the cured or final resin property requirements. To meet these objectives, hardeners may be used to accelerate curing once the resin is set and to optimize the resin properties. However, the placement of the epoxy in the subterranean formation is the critical and limiting step to the effective use of these systems in such formations.
Techniques for the placement of epoxy materials into subter, ranean formations; e.g., a casing annulus a gravel pack completion, or formations of the types described in U.S. Pat. Nos. 4,072,194 and 4,438,976, have been disclosed in numerous publications. All of these methods require that the epoxy material remain as a low viscosity fluid prior to and during the placement. Once in place, the epoxy must rapidly harden to form a rigid thermoset solid.
The principal manner of controlling the liquid epoxy viscosity and the hardening time of the epoxy is the selection of a hardener that is thermally activated. The increase in epoxy temperature caused by the thermal gradient in the well initiates the epoxy reaction once the activation or onset temperature of the hardener is exceeded. While variation in the hardener concentration provides a limited control of the set time, the amount of hardener used must be kept in a relatively narrow range for the resin to cure properly. With insufficient hardener, long set times result, incomplete reaction occurs, and resins remain uncured, If the amount of hardener is too great, the set time is too short to allow proper placement of the epoxy material. Also, with excessive amounts of hardener, the energy of the exothermic epoxy reaction is released very quickly. When this quick release of energy is coupled with the mass of resin required for many well operations, the energy released may produce extremely high temperatures in the resin. which can thermally decompose a portion of the epoxy material or damage underground equipment.